This invention relates to a process of silylation of object surfaces using a mixture of a silylation agent in admixture with an inert liquified gas, such as carbon dioxide.
As disclosed by W. Moreau, in Semiconductor Lithography, Plenum Press, 1987, pg 290, and Chapter 12, semiconductor surfaces or resist films can be modified by contacting and chemically reacting a silicon atom containing compound with the surface of a semiconductor resist film in a process called xe2x80x9csilylation.xe2x80x9d
For example, a silylating agent, such as hexamethyldisilazane (HMDS), reacts with the hydroxy groups present in a silicon dioxide-containing surface, such as xe2x80x9cSilanol,xe2x80x9d or the hydroxy groups present in a phenolic type resist, to form a silyl ether, e.g.:
xe2x80x94OH+(Me3Si)2NH______xe2x80x94OSiMe3+Me3SiNH2
The HMDS treatment of silicon wafers is commonly used as an adhesion promotion step prior to coating resists. The treatment of resist polymers is used to form bilayer or top surface imaging resists, as disclosed in U.S. Pat. Nos. 4,613,398, 5,366,852, 5,217,851, 4,981,909, K. Suguta, et al., Surface Silylation o DUV Lithography Jap. J. Appl. Phys., 39,669-674(2000), W. Hay, et al., Optimization of DUV Positive Tone Top Surface Imaging Process, Microelectronic Engineering, 23, 255-258 (1994) and E. Pavelcheck, et al., Process Techniques for Improving Performance of Positive Tone Silylation, Optical Engineering, 32, 2376-2381(1993).
In the process of treating a photoresist image, a sufficient wt % ( greater than 7 wt %) of silylating agent is incorporated therein to act as an in-situ mask for subsequent development of the underlying resist layer by reactive ion etching in oxygen.
The major drawback of silylation from the gas phase or liquid phase using agents such as HMDS is the swelling of the resist image which can be irreproducible in a semiconductor process especially across the surface of large diameter ( greater than 4 inch diameter) wafers.
For liquid phase silylation using agents such as HMCTS (hexamethylcyclotrisilazane) or HMDS, organic co-solvents, such as xylene, benzene, toluene, etc. are used to preswell the resist to aid in the diffusion of the HMCTS into the resist further swelling the resist images especially for nanolithography scale ( less than 500 nm images). The diffusion of organic liquids into a polymeric film are of the order of 10xe2x88x925 cm2/sec.
Supercritical fluids, i.e., fluids which are brought to highly elevated temperatures and pressures, are an order of magnitude lower in viscosity than organic liquids and have diffusitvities of 10xe2x88x924 to 10xe2x88x922 cm2/sec (See: M. Mc Hugh and V. Krukonis, Supercritical Fluid Extraction, Butterworths-Heineimann, 1994, pg. 15). For the purpose of this invention, xe2x80x9csupercritical fluidsxe2x80x9d embodies the fluids disclosed in the section of the Kirk-Othmer Encyclopedia of Chemical Technology, 3rd Edition, John Wiley and Sons, (1984) entitled: Supercritical Fluids, pages 872-877; as well as U.S. Pat. No. 5,508,510, the collective contents of which are hereby incorporated by reference herein.
According to U.S. Pat. No. 6,033,996 supercritical fluids of CO2 have been used to clean residues from resist surfaces.
Silylating agents are described in U.S. Pat 6,074,804, (Non amine silylating agent); U.S. Pat. No. 5,866,434, (Toluene flammable solvent used for silylation nanotube fibers); U.S. Pat. No. 6,042,993, (Diaminopropyldimethylsiloxane silylation agent); U.S. Pat. No. 6,063,974, (Zeolite silylation); U.S. Pat. No. 6,045,870 (Silylation of polymers containing hydroxyl, epoxy, acid groups); U.S. Pat. No. 6,099,960 (Silanol based silylating agents); U.S. Pat. No. 6,025,025 (Perfluoroalkylsilane for water repellency silylation); and U.S. Pat. No. 5,550,007 (bis dimethyaminosilane silylating agents). These agents are suitable for use in the present invention, and are hereby incorporated by reference herein.
Synthesis reactions using silylation of reactive hydroxy groups to form silanols and bulk synthesis reaction as disclosed in U.S. Pat. No. 5,157,139, are commonly used in conjunction with flammable solvents such as toluene, acetone, and xylene.
An inert or nonflammable media to silylate objects is desired. Easy recovery of the unreacted silylating agent is also desirable. Finally a resist based on silylation of polyhdroxystyrene as disclosed in U.S. Pat No. 4,689,288 (Silylated polyhydroxystyrene positive acid cat resist) illustrates using a synthetic silylation reaction of a polymer. The references cited above are hereby incorporated by reference herein.
The present invention relates to a method for silylation of such surfaces, found in films, fabrics, or workpieces which method utilizes a mixture of a silylation agent or other suitable organometallic reagent and a supercritical fluid or a liquified fluid.
More particularly, the instant invention relates to a process for rapidly treating photoresist films, semiconductor surfaces or other objects by using a mixture of a silylation agent and supercritical or liquified CO2 with or without some cosolvent therein.
In the case of resists, the present invention provides an enhanced process for silylation of resists after exposure in a top surface imaging or post-silylation treatment of a developed resist image.
In a typical prior art process, hexamethyl disilazane (e.g., as described in U.S. Pat. No. 4,613,398) is used to form an oxygen resistant image for dry developing. One major problem is the facile incorporation of the silylation agent sufficiently deep into the resist surface. Swelling agents have to be used in conjunction with the silylation agent to aid in the diffusion of the hexamethyl disilazane-type treatment.
As noted above, the use of a supercritical or liquified CO2 is used in conjunction with an organometallic reagent enhances, without swelling, the diffusion of the reagent into the film and provides unexpectedly higher resolution top surface imaging.
The process of the present invention can also be used to incorporate by silylation, silicon into an exposed resist, while simultaneously developing out a positive resist image using supercritical or liquified CO2 medium.
The instant process incorporates organometallic reagents in a mixture with supercritical or liquified CO2 and as noted, varying the pressure, time and temperature to achieve a higher resolution, or higher Si/organometallic incorporation into the resist film in a top surface or bilayer mode than heretofor achieved.
As a result of the discovery of the novel techniques of the instant process, an additional beneficial process has been developed whereby it is possible to use the instant silylation process carried out in a liquid fluid or a supercritical fluid as the solvent for the reaction media in the organic synthesis of a desired composition at the bulk level.